The parent application is for support of the IMMEDIATE (Immediate Myocardial Metabolic Enhancement During Initial Assessment and Treatment in Emergency care) Trial, a national randomized controlled clinical trial to test the impact of intravenous glucose, insulin, and potassium (GIK), for acute coronary syndromes. It is hypothesized that GIK, administered as early as possible in acute coronary syndromes, will reduce short-term (30- day) and long-term (1-year) mortality compared to usual treatment. The IMMEDIATE Trial also hypothesizes that the early use of GIK will reduce the incidence of life-threatening ventricular arrhythmias, and by mitigating infarct size in AMI, will help preserve left ventricular function and will thereby reduce the propensity for heart failure. A subsample of the IMMEDIATE Trial study population will comprise the "biologic mechanism cohort", and these subjects will return to the regional centers at 30 days after initial study enrollment for evaluation of infarct size, left ventricular function, and brain natriuretic peptide level. This application describes the core laboratory operations that will support this effort, and will generate the data used to test hypothesis H9: "In the biological mechanism sample, immediate GIK use will be associated with physiologic indicators reflecting a lower propensity for HF at 30 days including a) smaller infarct size by sestamibi perfusion imaging; b) better preserved LV function by gated SPECT imaging; and c) lower brain natriuretic peptide (BNP) levels." Thus the Specific Aims of this core laboratory application are: 1) to set up and support the study infrastructure required to generate information on infarct size and left ventricular function at the regional centers, and 2) to perform the blinded central analyses of the data in a high-quality manner consistent with current regulatory standards of handling electronic data in clinical trials. Infarct size will be assessed by a validated technique using sestarnibi SPECT imaging, and left ventricular function will be assessed by gated SPECT sestamibi imaging and measurements of brain natriuretic peptide levels. When completed, this will be the largest cohort ever studied examining the potential mechanisms of GIK effect. These data Will provide robust information with sufficient power to test the concepts in Hypothesis H9 of the parent trial and provide substantial insights into the mechanism of GIK effect.